/** Search only visible user/assistant text, never tool arguments or hidden reasoning. */
export function matchHistoryText(messages: unknown[], query: string): string | undefined {
  const needle = query.trim().toLocaleLowerCase();
  if (!needle) return;
  for (const value of messages) {
    if (!value || typeof value !== "object") continue;
    const message = value as Record<string, unknown>;
    if (message.role !== "user" && message.role !== "assistant") continue;
    const parts = Array.isArray(message.parts) ? message.parts : [message];
    for (const value of parts) {
      if (!value || typeof value !== "object") continue;
      const part = value as Record<string, unknown>;
      if (part.type !== "text" || typeof part.text !== "string") continue;
      const index = part.text.toLocaleLowerCase().indexOf(needle);
      if (index < 0) continue;
      const start = Math.max(0, index - 36);
      const end = Math.min(part.text.length, index + needle.length + 80);
      return `${start ? "…" : ""}${part.text.slice(start, end).replace(/\s+/g, " ")}${end < part.text.length ? "…" : ""}`;
    }
  }
}